That’s what a recent survey said (here). But less than 20% believe in alien abduction, so they are not a major terrorist threat. The study made no attempt to relate belief in aliens to religious beliefs. Slightly more Americans believe in global warming than in aliens (here for lots of details.) I suspect the two are (negatively) related. In any case, a lot more people believe in aliens than believe Trump is doing a good job. That’s something to be thankful for.